1. Field of the Invention
The present invention relates to an art for data access to a data storage area, and particularly relates to, for example, an art for reading the data from a logical volumes that are prepared on many disk storage units arranged in an array or writing the data on that logical volumes.
2. Description of the Related Art
For example, in a database system for the basic industries treating large volume of data, the data is managed by using a storage system that is configured separately from a host computer (hereinafter, simply referred to as a “host”). This storage system is also referred to as a disk array apparatus and this is a RAID (Redundant Array of Independent Inexpensive Disks) that is configured by arranging many disk storage units in an array.
For example, this storage system is as follows:
In other words, this storage system can receive a read/write command from the host, and further, it can hold a virtual disk as a virtual storage area. When receiving a write command from the host, if the virtual disk is defined as a control volume, the storage system may perform mirroring; and if the virtual disk is not defined as a control volume, the storage system may perform the operation for the normal reading or writing (for example, refer to a patent document 1).
[Patent Document 1]
JP-A-2000-112666
By the way, for example, one of the storage systems may prepare a plurality of logical volumes as the virtual storage area; and one of operating systems of the host (hereinafter, referred to as “a host OS”) may manage if the logical volume is in the online state or the offline state to each logical volume on the storage system. When the host OS receives a request of writing or reading processing of the data (hereinafter, referred to as “the I/O processing”) for a certain or user-desired logical volume (hereinafter, referred to as “a target volume”) from an application program of this host (hereinafter, referred to as “a host AP”), the host OS confirms if its target volume is in the online state or not. Then, if it is in the online state, the host transmits the I/O processing request for this target volume to the storage system; and if it is in the offline state, the host OS transmits an error response to the host AP. In other words, the host OS cannot read or write the data from or into the target volume unless the host OS is in the online state to the target volume.
However, a user may sometime want to read or write the data from or into the target volume that is in the offline state.
Specifically, for example, the storage system may perform the duplicating processing (so-called mirroring processing) so as to prevent the system from stopping even if the data is damaged due to a failure of the disk within the storage apparatus. According to such processing, the storage system has two logical volumes, namely, a primary volume and a secondary volume, and when receiving the writing request of the data from the host, the storage system duplicates the data that is requested to be written (hereinafter, referred to as “the write data”) and writes the same write data into both of the primary volume and the secondary volume.
In such duplicating processing, the primary and secondary volumes are generally managed in a pair state and they have the same volume label (for example, a volume name). Therefore, the host OS cannot differentiate the primary volume from the secondary volume that are managed in a pair state as a different volume. Thus, in the duplicating processing, one of the logical volumes, for example, the primary volume is in the online state by compulsion, the secondary volume is in the offline state, and the host OS is in the online state only for the primary volume.
However, the user may sometime want to perform the I/O processing for the secondary volume by operating the host AP. In order for this, the user separates the secondary volume from the primary volume by differentiating a volume label of the secondary volume from that of the primary volume, and then, further by restarting the host, so as to make the host OS to recognize the secondary volume. In other words, the user should separate the secondary volume from the primary volume by manual and make the secondary volume into the online state with the host OS.
Thus, in order to read or write the data from or into the logical volume in the offline, the troublesome processing is inevitable for the user.
In addition, for example, even if the user performs the above-described operation, a certain host OS may not be able to make the logical volume that is in the offline state into the online state.
Further, for example, in the duplicating processing, in order to make the secondary volume in the offline state to the host OS into the online state, this secondary volume should be separated from the primary volume. However, when the secondary volume is separated from the primary volume, the duplicating processing is not carried out, so that even if the write data is damaged, it is difficult to address this problem.
The above-described problem is not limited to the logical volume that is the virtual storage area and the physical storage area also involves such a problem.